The badly damaged Fukushima Dai-ichi nuclear power plant has been upgraded from 5 to 7 on the International Nuclear and Radiological Event Scale. That's, in case you were wondering, out of seven—the only other nuclear crisis to reach the same level is Chernobyl.

Authorities still believe "the cumulative amount [of radiation] from the Fukushima plant is less than that from Chernobyl," but another aftershock—6.6 magnitude—forced workers to evacuate on Monday, and Reactor No. 4 is apparently on fire.

Update: More information about the upgrade: The Wall Street Journal writes that the decision to upgrade the Fukushima plant's rating is a "grim admission" that we're talking about serious, long-term damage to the surrounding area, and an acknowledgment that the plant suffered from a "major release" of radioactive material. The Japanese government is evacuating towns as far as 19 miles away, depending on radiation levels, though the danger isn't immediate and residents have a month to move.